The present invention relates generally to drive systems for powering electric motors, and more particularly to a modular drive system designed and adapted for controlling motors of various sizes and ratings.
A myriad of applications exist in industry for electric motors of various types. In many applications, induction motors are driven to rotate loads, such as pumps, fans, conveyors, to mention only a few. Other types of motors may similarly be driven. A load may call for uniform speed and torque throughout its life, although many applications require much more flexible control. That is, a motor may need to be driven at different speeds and with different torques at different stages in its operation. To accommodate such needs, variable speed motor drives have been developed that allow for output waveforms of varying and controllable frequency, capable of correspondingly varying the speeds of driven motors. Similarly, equipment has been developed for soft starting motors, starting and stopping motors in controlled manners, and so forth. Such motor drives are now ubiquitous throughout industrial, commercial, shipping, material handling, and other applications.
In general, motor drives are designed to provide good service life in a range of conditions and with a range of loads. The drives may be designed around a single package that can be programmed and wired to receive input power as well as to output conditioned power to the electric motor. Such packaged products typically include power conditioning circuitry that receives alternating current (AC) input, and converts the AC input to a DC form, before reconverting the DC power to controlled frequency AC output. Various operator interfaces and programming platforms may also be provided, as well as networking capabilities.
One particular challenge that arises in such products is the design for various components of the package that allow for ease of manufacturing, while providing desired electrical properties, both for control level signals and for power signals. For example, low level logic signals will typically be used for certain control, such as on the order of 5 v DC or less, while higher voltage signals, such as on the order of 110 v AC, 220 v AC, or three-phase 440 v AC may be used for powering the driven motor. The actual voltages (and frequencies and currents) may vary depending upon the standards in the countries or areas where the equipment is used. However, all such equipment must accommodate both high and low level signals.
In many systems, optocouplers and similar signal isolation devices may be used to separate signals of different levels, particularly logic signals from power signals and boards. Such devices can add significantly to the cost of the equipment, particularly where multiple such devices are needed. Moreover, providing proper isolation and distances within the packages, such as between operator interfaces and powered circuit boards is always a challenge.
There is a need, therefore, for improved techniques for driving electric motors that can respond to such design challenges.